Bus riders and merchants along two of San Francisco's heaviest traveled corridors in San Francisco are clashing over a city proposal to create bus-only lanes on Van Ness Avenue and Geary Boulevard, with the possibility of putting light rail on Geary some day.

What could make the ride faster for public transit passengers also could clog up vehicular traffic, take away parking spaces, involve construction and scare away customers, according to some merchants who are wary of any road changes.

"As merchants, we have all the risk with no guarantee of a reward," said Jack Rhiel, co-owner of Big O Tires on Geary in the Richmond District. He cited the installation of light rail on Third Street, which snarls traffic and shop owners say hurts business.

The two roads the city has in mind for new bus-only lanes stretch across the city, east and west, north and south. Geary runs from the ocean, connecting a multiethnic stream of commuters to downtown and back. The 38 Geary bus line, said to be the busiest on the West Coast, serves 50,000 riders a day.

Meanwhile, Van Ness is the Highway 101 connector linking the Peninsula to the Golden Gate Bridge, the Mission to the marina, and has about 20,000 riders on city buses and lines originating outside San Francisco.

The idea to improve transit on those streets has been around for years, and advanced to neighborhood meetings last spring and this winter with the San Francisco Municipal Railway and the San Francisco County Transportation Authority. The Transportation Authority is the funding agency empowered by voters in 2003 to use part of the city sales tax to create exclusive transit lanes on Geary, Van Ness and Potrero Avenue, among other projects. Proposition K also provides funding to study whether Geary should get a light rail system.

But opponents say these projects were hidden within the lengthy text of Prop. K, and they are considering going back to voters to ask them to remove the section.

Merchants and residents "feel like the plan is being shoved down their throats," said David Heller, who owns a beauty supply store on Geary in the Richmond. He accuses the neighborhood's district supervisor and Prop. K proponent Jake McGoldrick of trying to pull a fast one.

McGoldrick said that residents for years have been calling for improvements on Geary. "When I was campaigning (in 2000), this was the No. 1 issue," McGoldrick said.

No final decisions have been made, and there will be more community workshops in the spring on what is called "bus rapid transit" to gather public opinions, said Tilly Chang, deputy planning director of the Transportation Authority.

The debates at previous meetings have been about whether the streets need dedicated bus lanes and whether the lanes should be on the right side or the middle of the road. And for Geary, whether the lane should be equipped with rail in anticipation of the day that the city gets enough money to put trains on the street. There are studies that still need to be done about how much parking could be lost -- or gained -- and how vehicular traffic might be impacted.

San Francisco already has some dedicated bus lanes, and the idea is gaining popularity around the country and in Canada. In San Francisco, the projects would include better bus stops for passengers to wait and traffic signal priority for buses so they spend less time stuck at red lights.

The Transportation Authority and rider advocates hope for a 15 to 30 percent reduction in travel time.

For Van Ness, the dedicated lane would run from Mission to Lombard streets and cost at least $100 million, paid for with local, state and federal dollars, Chang said. For Geary, it would run from Van Ness Avenue to 33rd and cost at least $150 million. The plans for Potrero Avenue are still rough.

The construction on Geary might be done by 2010 and on Van Ness by 2009, Chang said.

Ridership groups like Rescue Muni say the sooner the better. Rescue Muni is pushing hard for a dedicated middle lane that is rail ready on Geary. The street used to have the B-line rail, but it was abandoned in the 1950s.

Buses that run in the right lane are too slow, said Rescue Muni co-founder Andrew Sullivan. "They get caught up with right turns and parked cars and pedestrians crossing the street," he said.

On Tuesday, residents waiting for the 38-Geary said the bus is convenient but can take more than an hour to get downtown from the start of the line. Frequent rider Joe Delvecchio said the buses can be crowded, there is pick-pocketing, and a bus might not come for a long time, then two come together, bunched up.

Delvecchio cut the interview short when, sure enough, two 38s arrived at his stop at once. He guessed he had been waiting about 15 minutes.